1. Field of the Invention
The present invention relates to a capacitive sensor provided with a pattern of a light-transmissive conductive film containing metal nanowires.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2010-191504 discloses a touch switch of a capacitive sensor including a transparent conductive film having a monolayer structure. The touch switch disclosed in Japanese Unexamined Patent Application Publication No. 2010-191504 is composed of a touch electrode section and a wiring section of a meshed metal wire extending from the touch electrode. This touch switch configuration can be realized in compact touch panels, but in large-size panels, a large number of thin and long wirings are required to be arrayed. In addition, since the wiring section is made of a metal wire, the electrical resistance of the wiring section increases with lengthening and thinning the wiring section.
In the touch panel described in Japanese Unexamined Patent Application Publication No. 2009-146419, a plurality of transparent conductive structures constituted of carbon nanotubes are formed on a surface of a substrate. In addition, conductive wires formed of indium tin oxide (ITO) extend from the conductive structures. However, the conductive wire made of ITO or the like has increased electrical resistance, and the detection sensitivity is decreased due to the electrical resistance of the conductive wire.
In order to solve such a problem, films containing metal nanowires have been studied as light-transmissive conductive films having low resistance.
However, a case using metal nanowires in a light-transmissive conductive film having a monolayer structure has a problem in that the electrostatic discharge (ESD) tolerance is low compared with the case of ITO. The reasons thereof are, for example, (1) a light-transmissive conductive film containing metal nanowires has low electrical resistance compared with ITO, (2) even in the same pattern, a larger amount of current readily flows in ESD, (3) metal nanowires express conductivity in nano-size connection and therefore melt at a lower temperature compared with the melting point of the bulk metal (melt with the heat when a lot of current flows in a short time), and (4) the actual volume itself being in a conductive state is small.